Most bi-functional door latches have handles on either side of the door, a latching mechanism consisting of a bolt contained in a cavity that can alternately be extended into or retracted from an aligned orifice in the door jamb, and an opening in the door beneath the handle position communicating with the bolt cavity. Conventional door latches operate by simultaneous turning of a door knob in either direction to retract the bolt, and pushing or pulling to open the door. In push-pull type latches a push on the handle from the inside of the door and a pull on the handle from the outside of the door releases the bolt and opens the door in one continuous motion. Typically, the door opening between the handles contains a mechanism which translates the turning motion of the knob or the push-pull force on the handle into horizontal action to retract the bolt.
U.S. Pat. Nos. 6,293,598 and 7,258,374 disclose a push-pull type latch in which motion of the handle is translated to the bolt by a cam configured to engage a planar surface of the handle. Deflection of the handle is restricted by a stop, which is said to reduce wear on the moving components of the latch. The handle is under spring-loaded pressure so that when a pushed handle is released, the handle returns to its original position. Similarly, U.S. Pat. No. 4,629,228 discloses a complicated internal latch mechanism for displacing a bolt, utilizing a rotating cam responsive to deflection of the handle, and translated to the bolt by engagement of a driver tab on a slide member. U.S. Pat. Nos. 6,196,599, 5,085,474, and 4,003,593 describe further embodiments of push-pull type latches that utilize rotational components, such as a crank or cam internal to the door to translate push-pull vertical motion into horizontal movement of the bolt.
The afore-mentioned background art represent devices with several features in common, distinguishable from the present invention. These inventions all utilize mechanically sophisticated mechanisms internal to the door having moving parts to translate push-pull force on the handle to horizontal displacement of the bolt. This necessitates providing two holes in the door itself, one through the door to accommodate access of the handles to the motion translation mechanisms, and other hole to retain the bolt situated at a right angle to the first and communicating therewith. A second common feature is a requirement that the latch on either side of the door must be in the same corresponding geometric plane position on the door. Finally, these holes must be made very precisely in order to assure proper alignment of the latch components, so that installation thereof is not trivial or routinely performable by the end user.